Progress in Neuro-Psychopharmacology and Biological Psychiatry
Pain, aging and dementia: Towards a biopsychosocial model
Introduction
Dementia is a progressive disease associated with irreversible impairment and loss of cognitive abilities (Prince et al., 2013). Approximately 4.5–8% of people over seventy and 15–64% of people over eighty will experience dementia (Prince et al., 2013). As the population ages, the number of older people who experience dementia will also increase (Prince et al., 2013). There are several types of dementia, but differentiating them is beyond the scope of the present review [For a review of this topic, please see Scott and Barrett, 2007].
In the early 1990s, Marzinski (1991) and Hurley et al. (1992) were among the first to propose that discomfort, including pain, in people with dementia should be a focus of clinical and research attention. At that time, little was known about how pain and dementia impacted each other or even if people with dementia continued to experience pain.
We now know pain persists in dementia. Although there are wide ranging prevalence estimates, a recent systematic review concluded 46–56% of older people with dementia experience pain (van Kooten et al., 2016). Its prevalence does not appear to differ among dementia subtypes: Alzheimer's Disease (AD, 45.8%; 95% CI: 33.4–58.5), vascular dementia (56.2%; 95% CI: 47.7–64.4) and mixed AD and vascular dementia (53.9%; 95% CI: 37.4–70.1). These rates are comparable to estimates based on community-living cognitively intact older people (Shega et al., 2010). Within the same care settings, pain may be more (Bjork et al., 2016), less (Tan et al., 2015) or equally common (Lövheim et al., 2006) in those with dementia compared to those without dementia. We conclude, until further evidence is available, that the prevalence of pain among older people with dementia is comparable to other groups of older people.
It has been suggested that older people with dementia are at greater risk than those who are cognitively intact for inadequate pain management (McDermott et al., 2014; Monroe et al., 2012). For instance, a recent meta-analysis found nursing home residents with dementia receive fewer analgesics than residents who are cognitively intact, despite comparable numbers of diagnosed painful conditions (Tan et al., 2015). However, other reviews and empirical studies have found older people with dementia use more paracetamol (Corbett et al., 2014) and opioids (Jensen-Dahm et al., 2015a) than those without dementia. At present, it is not clear whether pain is undertreated in older people with dementia compared to older people who are cognitively intact. Careful analyses that simultaneously consider ability to report pain, the nature of potentially painful conditions, and the type and dosage of analgesics are needed.
Section snippets
Research in pain and dementia
As the subfield of pain and aging emerged, attention to older people with dementia grew (Gagliese, 2009). Clinically, much of the research focused on the development of behavioral observation scales. This work led to a plethora of assessment tools, none especially better than the others. Another stream of research focused on the documentation and management of pain in people with dementia in various care and residential settings. In parallel, there has been research into pain sensitivity and
Pain measurement in people with dementia
We begin with the biggest challenge in this field: valid pain assessment. Despite the surge in research attention, we have yet to establish the best way to assess pain in older people with dementia. As such, it is necessary to consider the impact of dementia on pain expression, whether verbal or behavioral, independently of its impact on the actual experience of pain (see Fig. 1).
The biological/sensory dimension of pain
Bearing in mind the caveats regarding assessment, we turn now to the research into pain and dementia and consider whether dementia impacts pain. In the biological/sensory domain, research has focused on dementia-related patterns in sensitivity to experimental and clinical pain. There has been little research into underlying mechanisms. Studies comparing sensitivity to experimentally applied painful stimulation between those with mild-to-moderate dementia and healthy controls are available. In
The affective dimension of pain
The psychological dimension of pain in dementia can be divided into affective and cognitive dimensions. It has been proposed that the affective dimension of pain in AD may be impacted earlier than the sensory dimension because limbic structures are affected earlier than the sensory cortex (Braak and Braak, 1995; Scherder et al., 2003). In response to different modalities of painful stimulation, older people with dementia report greater unpleasantness (Cole et al., 2006) and have greater
The social dimension of pain and dementia
Pain is also influenced by an array of social factors, including social support and the reactions of significant others to expressions of pain (Leonard et al., 2006; Mogil, 2015). Pain reports are communications that have impacts on both the person reporting the pain and the person receiving the report (Hadjistavropoulos et al., 2011; Mogil, 2015). Pain may be reported as a means of eliciting pain management, social support, and empathy or as a way of distancing others or excusing behavior. The
Integration among the dimensions: insights from imaging studies
The evidence reviewed above, despite its limitations, supports a biopsychosocial model in which pain and dementia have a reciprocal relationship. Support for the inter-relationships of the different dimensions of pain comes from studies of pain neural networks in people with dementia. Dementia, in particular AD, is associated with damage to multiple brain networks (Damoiseaux et al., 2012; Monroe et al., 2017), many of which overlap with the pain neuromatrix (Melzack, 2005, Melzack, 2001). As a
Conclusions and future directions
Although much more research is needed, a few conclusions can be drawn from the evidence we have reviewed. The most important are that about half of people with dementia, whether in community or institutional settings, report pain and that depression is a significant burden for many of these people. We have proposed that pain in older people with dementia is the result of an intricate network of interactions between three biopsychosocial phenomena and that dementia and pain have a reciprocal
Funding
This research did not receive any specific grant funding from funding agencies in the public, commercial, or not-for-profit sectors.
We thank the members of the Cancer Pain Research Unit Writing Seminar for thoughtful discussion of earlier drafts of this manuscript.
The authors have no conflicts of interest to declare.
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